Cologuard is a novel approach that looks for certain DNA mutations in a stool sample that are caused by precancerous polyps or cancerous tumors. Examining stool samples for cancer induced bleeding in the digestive tract are integral to the fecal immunochemical test (FIT), which is one of the more established colon cancer screening tests. The stool DNA approach taken by Cologuard performed exceedingly well in an extensive clinical trial that encompassed almost 10,000 participants. All trial participants provided samples for Cologuard stool DNA and FIT screenings and then underwent a colonoscopy. The trial results (which are discussed in this article - Multitarget Stool DNA Testing for Colorectal-Cancer Screening) found the Cologuard stool DNA screening test to materially outperform the FIT at detecting colon cancer and precancerous polyps. In the study, Cologuard detected colon cancers 92% of the time as compared to 74% for the FIT. Its sensitivity to detecting precancerous polyps was not as good as its effectiveness at detecting cancer, but it outperformed the FIT by a wide margin at these tasks too. Based on these trial results, it is easy to see why the FDA expert panel is recommending approval.
So what happens when Cologuard, or another stool DNA test, gets FDA approval? Probably not much at the outset. Many physicians will be compelled to prescribe it instead of the FIT because of its better accuracy. Of course, until health plans agree to cover stool DNA tests, patients will resist paying out of pocket for it. In due time, health plans will come around and agree to cover these new tests and once that happens, stool DNA tests will likely take market share from the blood based screening tests.
While the Cologuard clinical trial results indicate that it outperforms the FIT as a colon cancer screening test, no one should expect it to diminish the use of the conventional colonoscopy any time soon. Even as good as stool DNA screening results appear to be, they fall short of what a colonoscopy can do at detecting colon cancer and precancerous polyps. Stool DNA tests could put a dent in colonosopy volume one day if, with further refinement, they could get closer to 100% accuracy at screening for cancer and precancerous polyps, but that day is not is not imminent. Until then, the conventional colonoscopy will remain the gold standard for colon cancer screening.
For more information about your colon cancer screening options, visit the Colon Cancer Alliance.